The present invention relates to a method and a device for the continuous dosing of powdery substances, especially of powdery synthetic silica, by means of high-pressure gas.
The use of air-sprayed concrete (shotcrete) in building construction and foundation work, especially in tunnel construction, is known (cf. S+t 40, 1986, p. 3).
The setting action of air-sprayed concrete (shotcrete) is spontaneously increased by the addition thereto of synthetic silica, which is clearly noticeable in an increase of the adhering amount of concrete and a lesser rebound or fell off. The concrete removed from the wall displays a reduction in the degree of spreading or slumping of 20 to 25% compared to a concrete which contains no synthetic silica.
The addition and the exact dosing of the synthetic silica into the air-sprayed concrete (shotcrete) during application involves considerable problems. Thus, for example, the synthetic silica is conducted next to the concrete mass and the delivery air via a third supply line directly to the spraying nozzle.
However, the mixing which can be achieved thereby is totally insufficient, which can be noticed from the mist of silica at the exit point from the nozzle.
It would probably be more advantageous to add the silica directly into the stream of delivery air.
However, this can not be accomplished with the known pumps, such as e.g. Depa pumps because the pressure in the air line during operation is approximately 8 bars.